The field of the present invention is automatic variable ratio pulleys and particularly those used for automotive accessories or the like.
Conventionally, powered accessories, such as alternators, compressors for air conditioners, and pumps for power steering used on variable speed engines, have been driven from one end of the crankshaft of such an engine by means of pulleys, belts and the like. As a result, the accessories are rotated at velocities which are proportional, depending on the pulley reduction, to the rotating speed of the engine. In the case of automotive engines and the like, a great variation in speed is experienced by the engine and in turn the powered equipment.
It is necessary with such accessories to be driven at a minimum speed when the engine is running slowly. However, when the engine is sped up, the accessories are often driven much faster than necessary. The excessive speeds required of such accessories under such conditions are disadvantageous as they require additional power from the engine, they experience less reliability under such conditions, they generate additional unnecessary noise and they must be made stronger and more adaptable to the speed ranges.
Devices have been developed for driving accessories which include multiple ratios. Such devices include fixed multiratio transmissions employing automatic clutching mechanisms. Such devices provide a better compromise between engine speeds and accessory speeds. However, such devices can result in abrupt speed changes transmitted to the accessories when the ratios are changed. Under such conditons, the added forces of acceleration and deceleration contributed by the transmission must be considered in the design of drive belts and accessory components. Additionally, the high force loading on the clutch mechanisms in such devices can often result in high clutch wear and early failure.
Such transmissions for auxiliary equipment drives have also included variable diameter sheaves which are typically responsive to the action of centrifugal weights, hydraulic pressure or the like. Such devices can reduce the shock loading of fixed ratio devices. However, they do not normally include a means for providing feedback to the control device as to the effective sheave diameter. Consequently, the sheave diameter is not easily controlled, particularly when stepless ratio operation is to be employed rather than fixed set ratios. Additionally, many devices require complicated mechanisms for achieving the appropriate speed to sheave diameter response or simply provide stepped stations, effecting stepped fixed ratio operation.